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Fluid structure interaction in ANSYS-CFX

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Old   February 12, 2011, 16:00
Question Fluid structure interaction in ANSYS-CFX
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Amol
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Hello everybody,
i am doing flutter analysis with two way FSI, coupling ANSYS(transient analysis system) and CFX. structural domain is panel of 5 mm thickness and fluid has supersonic flow above it. now problem is that when i am keeping large deflection ON in mechanical part of the ANSYS (i.e. by doing this i am considering geometric non linearity in panel) panel shows nice limit cycle oscillations in it (of amplitude 0.004 m without giving any initial disturbance to panel). but when i am doing same simulation with keeping large deflection OFF (i.e. geometric nonlinearity removed) it should show large deflections in panel instead of limit cycle oscillations. but don't know why i am getting very small deflections in panel (amplitude of just some nanometer). what might be going wrong?? please help................
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Old   February 22, 2011, 12:52
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Ji Pei
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I have the same question! I did a FSI calculation for a water pump impeller, and it seems to be linear problem(0.1-0.5mm deflection according to the test). So I have tried to keep large deflection off, the values are small, like 100 times less than experiment. One way coupling seems right. When I keep large deflection on, the deflection curve is not quite right. It is confusing! So I want to know, what has happened in software when large deflection is off.
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Old   April 4, 2011, 01:08
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vahid
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Hello
I have the same problem and the structure (a long plate behind a rigid cylinder) has very little cross flow oscillation due to the vortex shedding.
it would be very helpful if any body has got the reason .

thanks
V.T
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Old   April 4, 2011, 09:49
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Edmund Singer P.E.
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Large deflections must be on for 2way FSI. Loads will be always applied to non-deformed body (within Mechanical Ansys) if large deflections are not on.
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Old   April 4, 2011, 12:18
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Amol
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Quote:
Originally Posted by singer1812 View Post
Large deflections must be on for 2way FSI. Loads will be always applied to non-deformed body (within Mechanical Ansys) if large deflections are not on.
even though the load is applied on non deformed bodies when we keep geometric nonlinearity OFF, what is the reason to get small deformations in structures as compared to the case when we keep geometric nonlinearity ON.
Is there any other option available in mechanical ANSYS while doing 2 way FSI using ANSYS-CFX????
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